Previously, the adding of various kinds of water-insoluble photographic additives to a photographic emulsion has been done by dissolving the additives in an organic solvent such as methanol. The resulting solution is then added to a silver halide emulsion. However, the use of an organic solvent in such a method causes the problem that condensates are produced in the photographic emulsion, and is attended with the defect that massive and streaky coating troubles are caused when the photographic emulsion is coated.
Instead of using such a conventional method, a method has been attempted in which an aqueous dispersion is prepared by dispersing photographic additives into an aqueous solution system in the presence of a wetting agent or a dispersing agent without using any organic solvents and the resulting dispersion is added to a silver halide emulsion.
For instance, Japanese Patent Application (OPI) No. 110012/77 (corresponding to British Pat. No. 1,570,362) (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") discloses a process wherein a sensitizer is ground to fine grains in an aqueous phase in the presence of a dispersing agent having a definite surface tension (surface active agent), water is removed from the aqueous dispersion obtained, the resulting matter is dried and then added to a silver halide emulsion as it is or after it is dispersed in water or a gelatin aqueous solution.
Japanese Patent Application (OPI) No. 102733/78 (corresponding to U.S. Pat. No. 4,140,530) describes a method wherein a homogeneous mixture comprised of finely granulated photographic additives, a dispersing agent such as sorbitol, gelatin and so on (paste mixture) is prepared. The mixture is molded in the form of noodle, and dried with hot air to obtain a granulated matter. The granulated matter obtained is, then, added to a photographic aqueous colloid coating composition.
U.S. Pat. No. 4,006,025 describes a method wherein a spectral sensitizing dye is mixed with water to make a slurry. The resulting slurry is heated to a temperature of 40.degree. to 50.degree. C. and dispersed homogeneously into water in the presence of a surface active agent using a homogenizer or a milling machine. The thus obtained dispersion is then added to a silver halide emulsion.
Although these addition methods each relates to a method of dispersing photographic additives (such as spectral sensitizing dyes) in an aqueous system without using any organic solvents, in practice the methods have the following problems. Since an aqueous dispersion is powderized by a freeze-drying technique or the like, the time required to make photographic additives (such as spectral sensitizing dyes) adsorb on silver halide grains is elongated. Accordingly, the desired photographic sensitivity cannot be attained in a short time. Further, such an emulsion will frequently cause coating troubles due to precipitates, if it is ever coated. In addition, a wetting agent or a dispersing agent used at the time of dispersion of photographic additives causes the destruction of an emulsified matter present in a silver halide emulsion, has adverse effects on the high speed coatability of the silver halide photographic emulsion (for example, causes an increase in coating trouble) and, further, causes deterioration of adhesiveness among constituent layers of the silver halide photographic material produced and in its turn, leads to the manufacture of undesirable products.